In recent years, hands-free call systems, which allow drivers to speak over mobile phones without holding a mobile phone in their hands, have become common. In addition, in a hands-free call system, use of a plurality of microphones allows a plurality of speakers to talk with a person at far end. In this case, to transmit clearly speech that is uttered and captured to a person on the other end, the microphone through which the speaker inputs uttered speech needs to be properly identified.
For example, Patent Literature 1 discloses a technique for identifying a microphone through which a speaker inputs uttered speech from among a plurality of microphones. In the system disclosed in Patent Literature 1, a microphone whose input level has continued to be above a threshold value for not shorter than a predetermined time period after input of uttered speech by a speaker is identified as a microphone associated with the position of the speaker from among a plurality of microphones. Use of this identifying method in a hands-free call system allows a microphone through which a speaker has input uttered speech to be appropriately identified from among a plurality of microphones.
In addition, in the system disclosed in Patent Literature 1, a background noise level in the vicinity of each microphone is measured in advance, the background noise levels of the respective microphones are corrected to match a background noise level in a whole room, and a microphone associated with the position of a speaker is then identified. This allows identification that is not affected by the background noise levels of the respective microphones.